CORE: perform post-condition in algorithm_do_this() under all circumstances

CORE: perform post-condition in algorithm_do_this() under all circumstances

When ossl_provider_query_operation() returned NULL, the post-condition
callback wasn't called, and could make algorithm_do_this() falsely
tell the caller that there was an error.  Because of this, a provider
that answered with NULL for a particular operation identity would
effectively block the same query on all following providers.

Fixes #12293

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/12365)